Chemical & Process Engineering ‘Engineering from Molecules’ Water sector applications: Microbubble applications: wastewater aeration, dispersed air flotation,

Chemical &ProcessEngineering

‘Engineering from Molecules’

Water sector applications: Microbubble applications: wastewater aeration, dispersed air flotation, ozone dosing, digester/algal growth/carbon capture.Fluidic electricity generation

Will ZimmermanProfessor of Biochemical Dynamical SystemsChemical and Process Engineering, University of Sheffield

Chemical &ProcessEngineering ‘Engineering from Molecules’


Outline

• Why microbubbles: mass transfer and flotation

• Wastewater aeration

• Potential for replacing dissolved air flotation

• Algal growth / carbon capture / wastewater plant integration => target energy positive and CO2 neutral

• Ozone

• Fluidic electricity generator



Why microbubbles?

• Faster mass transfer -- roughly proportional to the inverse of the diameter• Flotation separations -- small bubbles attach to particle / droplet and the whole floc rises

Steep mass transferenhancement.



Fluidic oscillator

Fluidic oscillatorNo moving parts switching



Pilot scale: Experimental design

Suprafilt layout for 30m^3/h Master-slave amplifier system for fluidic oscillator



Energetics: Power consumption

Oscillatory flow draws less power than steady flow at the same throughput!



With Oscillator

Without OscillatorWith Oscillator, Master (small) shut completely

Visualization studyand Frequency analysis



Frequency of oscillation depends on feedback loop and air throughput



Aeration: DO profiles, clear water Blow-up



Delay time and dosage

0

1 TD C dt

T



Summarized findings

• Visualization study

• Oscillation frequency

• power consumption: with maximum value of 18% reduction at the best aeration configuration.

• Clear water dissolved oxygen study: 3-4 fold better dosage at 83% of the design volumetric flow rate.

• SBR planned next in Rosslare – two basins with automatic control. KTP with ADB and YWS.



Potential for dissolved air flotation (DAF) plant

• Potentially eliminate recycle flow and saturator load (90-95% electricity cost)

• Uses blowers not compressors/saturators (much lower capital)

• Cheap materials for retrofit with fluidic oscillators introduced in the plumbing and manifolds to diffuser bank for dispersal.



Microporous diffusers

• Original nickel-based microporous membrane ~£2k /m2

• Now works with microporous ceramic ~£200-300 / m2

Suprafilt and HP Technical Ceramics are collaborating with UoS on fabrication



Field trial campaign

• Agreed with Northern Ireland Water and AECOM Design Build (Brenda Franklin) to trial the technology in a single DAF cell at Carmoney WTW which is undergoing refurbishment

• Trial to be conducted August 2010.• 12m2 of surface area available for microporous diffuser

insertion for retrofit. Unit instrumented to measure performance and to be outfitted with visualization equipment.

• Tune performance in operating parameters – chiefly air throughput rates, water flow rate (~cm/s) and oscillation frequencies.

• Model data from performance studies for engineering design parameters (number of plate diffusers, placement, flow rates).

• Gain operational experience – identify potential problems, risks, failure modes -- to plan maintenance regime.

• Assess CAPEX and OPEX requirements

Microporousdiffuser

Growing algaewith microbubbles



Ozone plasma microreactors

• How ozone disinfects in water solutions.

• The ozone plasma microreactor in the lab

• How to get the ozone off the chip? Microbubbles!

• Prototypes

• Field trial campaign



Ozone Kills!

Ozone dissolves inwater to producehydroxyl radicals

Hydroxyl radical attacks bacterial cell wall, damages it by ionisation, lyses the cell (death) and finally mineralises the contents.

One ozone molecule kills one bacterium in water!



Ozone plasma microreactor in the lab.

Upper plate

Lower plate

Electrodes

Electrical connection

Fibre optics

Chipholder construct



Microfluidic onchip ozone generation

Our new chip design and associated electronics produce ozone from O2

with two key economic features:

1. Low power. Our estimates are a ten-fold reduction over conventional ozone generators.

2. High conversion. The selectivity is double that of conventional reactors (30% rather than 15% single pass).

Additionally, it works at atmospheric pressure, at room temperature, and at low voltage (170V, can be mains powered).

Emission UV-Vis spectrum of exit gas with clear O3 signature. Analysis suggests 30% conversion at

temperature 350K.



Plasma disks

• 25 plasma reactors each with treble throughput over first microchip



Dosing lance prototypes

Axial view of the old lanceWith 8 or 16 microdisc reactors

New lance = 70 microdisc reactorsQuartz for UV irradiation



Corporation cock assembly

Ball valve External assembly.

Valve control to toggle for flow/no flow



WTW tests on raw water

Raw water inlet

Upstream sample point for benchmarking water qualityand corporation cock to be fitted

Downstream sample point for turbidity measurements. Sufficient for water quality study.



Potential markets

• Water purification (municipal)

• Waste water – organics removal

• Waste water – disinfection before release

• Sterilization (medical, biotech, pharmaceutical)

• Distributed / remote / portable water purification

• Ventilation system sterilization

• Gas analysis (ozonolysis) and sensors



Air lift loop bioreactor design

Schematic diagram of an internal ALB with draught tube configured with a tailor made grooved nozzle bank fed from the two outlets of the fluidic oscillator. The microbubble generator is expected to achieve nearly monodisperse, uniformly spaced, non-coalescent small bubbles of the scale of the drilled apertures.

• Journal article has won the 2009 IChemE Moulton Medal for best publication in all their journals.• Designed for biofuels production• First use: microalgae growth• Current TSB / Corus / Suprafilt grant on carbon sequestration feasibility study on steel stack gas feed to produce microalgae.



Construction

Body / side view

Top with lid

Inner view:Heat transfercoils separatingriser /downcomer.

Folded perforated Plate -bubblegenerator.Replaced bySuprafilt 9inch diffuser



ALB for algae growth



Results

Rapid pH dropPotential licensee for carbonSequestration organic chemistry

30% higher relative growth rate with only60 minutes per day dosing TSB / Corus / Suprafilt project for continurous dosing.

Best poster 6th Annual bioProcessUKConference, Nov 2009, York.



Current programme of field trials

• Corus: steel plant algal culture

• Aecom: separation/harvesting

• Air lift loop bioreactor development for biofuels

Approximately 1 cubic metrecube design with0.8 m2 square ceramic microporousdiffusers.



Prospects for process integration / intensification for WWTW flowsheet re-design

Key concept: Microbubble dosing will be cheap, but allow access to all process gases.

Anaerobic digestor:

CO2 dosing and CO2/CH4 stripping

Accelerates biochemistry

CHP provides CO2 for algal growth

Anammox process

Stage 1 Aerobic (air dosing)

Stage 2 Anaerobic CO2 dosing and CO2/N2 stripping

Result: Accelerate biochemistry of all processes by reactive extraction. Influence production by nutrient dosing rate. Grow algae for biomass / biofuel. Sequester CO2. Provide O2.



Remote fluidic electricity generator

• Concept: Fluidic oscillator provides “AC” fluidic power. Piezoharvester converts to AC electricity.

• Need: remote pipelines for parasitic electricity generation from flow energy.

• No moving parts, fit and forget, power sensors and telemetry, potentially actuators.

• German group published results in December 2008. Found 150microWatts from flows rates typical of tap water.

• We have a similar approach but with our key feature have been able to achieve 1.5mW with same flow rates and can apply standard approach for another factor of 5-10 increase.



Potential microbubble markets• Dispersed air flotation for solids removal in water and

wastewater (achieved target bubble size, 20 microns)

• Wastewater aeration (partner YW, 18% energy reduction, 3-fold higher dosing rates on retrofit)

• Algal biomass / bioenergy production (partner Corus, >30% extra biomass from CO2 microbubble dosing)

• Wastewater treatment processes integration and intensification: aeration, digestion, de/nitrification, algal growth. Targets: smaller footprint; carbon and energy neutral!

• Ozone dosing from a plasma microreactor dosing lance

• Air lift loop bioreactor development for biofuels

• Heterogeneous chemical and bioreactor engineering, gas-lift oil recovery, oil-water separations, heat transfer

Documents

Chemical & Process Engineering ‘Engineering from Molecules’ Water sector applications: Microbubble applications: wastewater aeration, dispersed air flotation,